The goal of this SBIR project is the development of an improved inorganic ion exchanger with an extremely high selectivity for Sr2+. This ion exchanger will improve the extraction of 90Sr from groundwater at the sites around the US and the world that have become contaminated through mishap or poor handling of nuclear materials, some of which are in contact with aquifers and bodies of water used as drinking water supplies. 90Sr is a ?-emitting isotope with an extremely low maximum safe exposure limit. (The drinking water limit is 8 pCi/L.) Development of this material will make a significant contribution to safer drinking water. In Phase I of this project we demonstrated that the substitution of SnlV and SilV for part of the SbV in the pyrochlore-structured antimonic acid (Sb2O5 4 H2O) increased both the compound's affinity for Sr+2 and its selectivity for strontium over calcium by a factor of nearly four. (A strong preference for Sr+2 is important, because the strontium is always found with a large excess of calcium.) The resulting material has a capacity for 90Sr over 200 times that of the clinoptilotile currently used to collect strontium in pump-and-treat systems. In Phase II we will refine the composition of the exchanger and scale-up the synthesis. The material will be evaluated in complete detail for use as a column material for extracting 90Sr from ground water out of the ground or as the active component in a permeable reactive barrier to block the motion of 90Sr in ground water in the ground. In plain language: Adding tin or silicon to antimonic acid greatly improves its ability to remove strontium from aqueous solutions in the presence of the very similar calcium. This makes it an excellent choice for removing radioactive strontium-90 from ground water either at the surface, or while still in the ground. [unreadable] [unreadable] [unreadable]